[Mailman-Users] join list - receive digest instead of regular via email

[Dave B]

I have a list set up where the default for joining is Regular. People 
sign up via a php form on our website that then emails to 
"listname-join at domain.org". I need to give them the option of receiving 
Regular or Digest in this form. Is there a way via email to join them 
to the Digest even though Regular is the default?

Something along the lines of "listname-join-digest at domain.org"? I'd 
like to keep this as transparent to the end user as possible and not 
make them go the list web page to change their subscription status.

Thanks - Dave Bevis